The Linux Operating System

Overview

• What you’ll learn: The fundamentals of the Linux operating system, including the kernel, distributions, and the Ubuntu Server ecosystem.
• Prerequisites: None
• Estimated reading time: 15 minutes

Introduction

Linux is one of the most widely used operating systems in the world, powering everything from smartphones and embedded devices to the vast majority of servers on the Internet. Unlike proprietary operating systems such as Windows or macOS, Linux is open-source software, meaning its source code is freely available for anyone to view, modify, and distribute.

Understanding Linux is an essential skill for system administrators, DevOps engineers, and software developers. In this lesson, we will explore what Linux is, how its architecture is organized, the concept of distributions, and why Ubuntu Server is an excellent choice for production environments.

By the end of this lesson, you will have a solid understanding of the Linux ecosystem and be ready to start working with the command line in subsequent lessons.

What is Linux?

Linux, in the strictest sense, refers to the Linux kernel — the core component of the operating system that manages hardware resources, process scheduling, memory management, and device drivers. The kernel was originally created by Linus Torvalds in 1991 and has since grown into one of the largest collaborative software projects in history.

When most people say “Linux,” they are referring to a complete operating system that combines the Linux kernel with a collection of user-space utilities, libraries, and applications. This complete package is more accurately called a GNU/Linux system, as many of the essential utilities come from the GNU Project.

Kernel vs. User Space

The Linux architecture is divided into two main areas:

• Kernel space: The privileged area where the kernel runs. It has direct access to hardware, manages memory, schedules processes, and handles system calls from user-space programs.
• User space: Where all user applications and services run. Programs in user space cannot directly access hardware; instead, they make requests to the kernel through system calls.

$ uname -r
5.15.0-91-generic

$ uname -a
Linux ubuntu-server 5.15.0-91-generic #101-Ubuntu SMP x86_64 GNU/Linux

The uname command displays information about the running kernel. The -r flag shows the kernel release version, while -a displays all available system information.

Linux Distributions

A Linux distribution (or “distro”) is a complete operating system built around the Linux kernel. Each distribution packages the kernel together with a specific set of software, a package manager, configuration tools, and sometimes a desktop environment. Popular distributions include:

• Ubuntu: Based on Debian, known for ease of use and extensive documentation. Available in Desktop and Server editions.
• Debian: One of the oldest distributions, known for stability and its massive software repository.
• CentOS / Rocky Linux / AlmaLinux: Enterprise-grade distributions compatible with Red Hat Enterprise Linux (RHEL).
• Fedora: A cutting-edge distribution sponsored by Red Hat, often used as a testing ground for RHEL features.
• Arch Linux: A rolling-release distribution aimed at experienced users who want full control over their system.

Each distribution has its own package management system. Debian-based systems (including Ubuntu) use apt and .deb packages, while Red Hat-based systems use dnf (or yum) and .rpm packages.

Ubuntu Server

Ubuntu Server is a variant of the Ubuntu distribution designed specifically for server environments. It ships without a graphical desktop by default, providing a minimal installation optimized for performance and security.

Key Features

• LTS Releases: Ubuntu offers Long Term Support releases every two years (e.g., 22.04 LTS, 24.04 LTS). LTS versions receive security updates and bug fixes for five years, making them ideal for production servers.
• Snap packages: Ubuntu supports Snap, a universal package format that bundles applications with their dependencies for consistent deployment.
• Cloud-init: Built-in support for cloud instance initialization, making Ubuntu Server a popular choice on AWS, Azure, and GCP.
• Extensive documentation: The Ubuntu Server Guide provides comprehensive coverage of common server administration tasks.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 22.04.3 LTS
Release:        22.04
Codename:       jammy

$ cat /etc/os-release
NAME="Ubuntu"
VERSION="22.04.3 LTS (Jammy Jellyfish)"
ID=ubuntu
ID_LIKE=debian

Server vs. Desktop

The key differences between Ubuntu Server and Ubuntu Desktop are:

• No GUI by default: Server edition uses the command line exclusively, reducing resource usage.
• Different default packages: Server includes tools like OpenSSH server, while Desktop includes a graphical desktop environment.
• Kernel tuning: The server kernel may be configured with different scheduler settings optimized for throughput rather than interactivity.

Getting Help

Linux provides several built-in mechanisms for getting help directly from the command line:

$ man ls
LS(1)                     User Commands                    LS(1)

NAME
       ls - list directory contents

SYNOPSIS
       ls [OPTION]... [FILE]...

$ ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).

$ info coreutils
GNU Coreutils reference documentation...

• man pages: The manual pages are the primary documentation system on Linux. Use man <command> to read the full manual for any command.
• --help flag: Most commands support a --help flag that prints a brief usage summary.
• info pages: Some GNU utilities provide more detailed documentation through the info system.
• apropos: Search man pages by keyword. For example, apropos partition finds all man pages related to partitioning.

Key Takeaways

• Linux refers to the kernel; a complete OS is a Linux distribution combining the kernel with user-space tools.
• The architecture is split into kernel space (hardware access, process management) and user space (applications, services).
• Distributions like Ubuntu, Debian, CentOS, and Arch each package Linux differently with their own tools and philosophies.
• Ubuntu Server LTS releases provide five years of support and are widely used in production and cloud environments.
• Built-in help is always available through man, --help, info, and apropos.

What’s Next

In Lesson 2, you will learn about Shell Navigation and File System, including how to use the bash shell, navigate directories, and work with files using essential Linux commands.

$ uname -r
5.15.0-91-generic

$ uname -a
Linux ubuntu-server 5.15.0-91-generic #101-Ubuntu SMP x86_64 GNU/Linux

$ uname -r
5.15.0-91-generic

$ uname -a
Linux ubuntu-server 5.15.0-91-generic #101-Ubuntu SMP x86_64 GNU/Linux